(i) Field of the Invention
The present invention relates to a method for driving an ink jet print head installed in electronic equipment such as printers, word processors, facsimile machines and plotters.
(ii) Description of the Related Art
FIG. 6 shows an embodiment in which a driving method usually used in a thermal print head having a relatively low print density is directly applied to an ink jet print head. In the embodiment of FIG. 6, a print dot unit is 2 dots/mm and the print density is 8 dots/mm, and print dots of 12 nozzles 11 (A to L) provided in an ink jet print head 10 are illustratively represented by alphabetic characters corresponding to alphabetic characters attached to the respective nozzles 11. In this embodiment, each of these nozzles 11 prints 4 dots. In the first print line on a print paper, the head 10 is moved one dot at a time by 4 dots in one print scanning direction (in a right direction in the drawing) from a print motion starting point (the left edge of the drawing). At this time, printing is carried out by the predetermined nozzles 11 in accordance with print information. When the printing of this first print line has terminated, the head 10 has been shifted (to the fifth dot) to the right side by 4 dots.
Next, the print paper is advanced one print line, and printing is then done, while the head 10 is moved one dot at a time by 4 dots in another print scanning direction (in a eft direction in the drawing). Here, the printing of the second print line is completed, and the head 10 is returned to the print starting point. Afterward, the reciprocating motion is similarly carried out in the print scanning directions every two print lines.
If a print time for one print line in the printing operation in FIG. 6 is 5 ms, a time required for one reciprocating motion of the head 10 (hereinafter referred to as "a shuttle driving cycle at times", (see a symbol T' in FIG. 6) is 10 ms, and a shuttle driving frequency is 100 Hz.
In the case that a driving method of a thermal print head having a relatively low density is directly applied to an ink jet print head, an ink jet print head must be operated at the above-mentioned shuttle driving cycle and driving frequency. However, for the ink jet print head, the driving cycle is very short and the driving frequency is fairly high, and therefore vibration is generated during the printing operation, so that printed letters are disordered and bubbles are introduced into an ink which gives rise to undesirable lack of emergence of the ink.
Furthermore, since a time of from the completion of the printing in one print line to the start of the printing in the next print line, i.e., a time required for a paper feed is longer than a pulse cycle of ink discharge (which corresponds to a cycle of ink adhesion to the paper, i.e., the time it takes for the ink to hit the paper), a movement speed of the shuttle (the head 10) is not constant. In consequence, the operation of the shuttle is stiff, which has a bad influence on a print quality.